The present invention relates to the field of communications, and more particularly, to feedthrough lens antennas.
Existing microwave antennas include a wide variety of configurations for various applications, such as satellite reception, remote broadcasting, or military communication. The desirable characteristics of low cost, light-weight, low profile and mass producibility are provided in general by printed circuit antennas. The simplest forms of printed circuit antennas are microstrip antennas wherein flat conductive elements are spaced from a single essentially continuous ground element by a dielectric sheet of uniform thickness. An example of a microstrip antenna is disclosed in U.S. Pat. No. 3,995,277 to Olyphant.
The antennas are designed in an array and may be used for communication systems such as identification of friend/foe (IFF) systems, personal communication service (PCS) systems, satellite communication systems, and aerospace systems, which require such characteristics as low cost, light weight, low profile, and a low sidelobe.
The bandwidth and directivity capabilities of such antennas, however, can be limiting for certain applications. While the use of electromagnetically coupled microstrip patch pairs can increase bandwidth, obtaining this benefit presents significant design challenges, particularly where maintenance of a low profile and broad beam width is desirable. Also, the use of an array of microstrip patches can improve directivity by providing a predetermined scan angle. However, utilizing An array of microstrip patches presents a dilemma. The scan angle can be increased if the array elements are spaced closer together, but closer spacing can increase undesirable coupling between antenna elements thereby degrading performance.
Furthermore, while a microstrip patch antenna is advantageous in applications requiring a conformal configuration, e.g. in aerospace systems, mounting the antenna presents challenges with respect to the manner in which it is fed such that conformality and satisfactory radiation coverage and directivity are maintained and losses to surrounding surfaces are reduced. More specifically, increasing the bandwith of a phased array antenna with a wide scan angle is conventionally achieved by dividing the frequency range into multiple bands.
One example of such an antenna is disclosed in U.S. Pat. No. 5,485,167 to Wong et al. This antenna includes several pairs of dipole pair arrays each tuned to a different frequency band and stacked relative to each other along the transmission/reception direction. The highest frequency array is in front of the next lowest frequency array and so forth.
This approach may result in a considerable increase in the size and weight of the antenna while creating a Radio Frequency (RF) interface problem. Another approach is to use gimbals to mechanically obtain the required scan angle. Yet, here again, this approach may increase the size and weight of the antenna and result in a slower response time.
Thus, there is a need for a lightweight phased array antenna with a wide frequency bandwidth and a wide scan angle, and that is conformally mountable to a surface. Moreover, there is also a need for feedthrough lens antennas having such characteristics. Feedthrough lens antennas may be used in a variety of applications where it is desired to replicate an electromagnetic (EM) environment present on the outside of a structure within the structure over a particular bandwidth. For example, a feedthrough lens may be used to replicate signals, such as cellular telephone signals, within a building or airplane which may otherwise be reflected thereby. Furthermore, a feedthrough lens antenna may be used to provide a highpass filter response characteristic, which may be particularly advantageous for applications where very wide bandwidth is desirable.
An example of such a feedthrough lens antenna is disclosed in the above patent to Wong et al. The feedthrough lens structure disclosed in this patent includes several of the multiple layered phased array antennas discussed above. Yet, the above noted limitations will correspondingly be present when such antennas are used in feedthrough lens antennas.
In view of the foregoing background, it is therefore an object of the invention to provide a feedthrough lens antenna having a wide bandwidth and a wide scan angle.
This and other objects, features and advantages in accordance with the present invention are provided by a feedthrough lens antenna including first and second phased array antennas and a coupling structure connecting the first and second phased array antennas together in back-to-back relation. Each phased array antenna may include a substrate and an array of dipole antenna elements thereon. Each dipole antenna element may include a medial feed portion and a pair of legs extending outwardly therefrom. Additionally, adjacent legs of the adjacent dipole antenna elements may include respective spaced apart end portions having predetermined shapes and relative positioning to provide increased capacitive coupling between the adjacent dipole antenna elements.
More specifically, the coupling structure may include a ground plane. Each phased array antenna may have a desired frequency range, and the ground plane may be spaced from each array of dipole antenna elements less than about one-half a wavelength of a highest desired frequency. The coupling structure may also include a plurality of transmission elements each connecting a corresponding dipole antenna element of the first phased array antenna with a dipole antenna element of the second phased array antenna. The plurality of transmission elements may be coaxial cables, for example.
The feedthrough lens antenna may also include at least one dielectric layer on each array of dipole antenna elements. Each leg may include an elongated body portion and an enlarged width end portion connected to an end of the elongated body portion. Additionally, the spaced apart end portions in adjacent legs may include interdigitated portions. More particularly, each leg may include an elongated body portion, an enlarged width end portion connected to an end of the elongated body portion, and a plurality of fingers extending outwardly from the enlarged width end portion.
Additionally, each phased array antenna may have a desired frequency range, and the spacing between the end portions of adjacent legs may be less than about one-half a wavelength of a highest desired frequency. Each array of dipole antenna elements may include first and second sets of orthogonal dipole antenna elements to provide dual polarization. The elements of each array of dipole antenna elements may also be sized and relatively positioned so that each phased array antenna is operable over a frequency range of about 2 to 30 GHz, for example. Further, the elements of each array of dipole antenna elements may be sized and relatively positioned so that each phased array antenna is operable over a scan angle of about xc2x160 degrees, for example.
A method aspect of the present invention is for making a feedthrough lens antenna. The method may include providing first and second substrates, forming an array of dipole antenna elements on each of the first and second substrates to define first and second phased array antennas, and connecting the first and second phased array antennas together in back-to-back relation. Each dipole antenna element may include a medial feed portion and a pair of legs extending outwardly therefrom. Respective spaced apart end portions of adjacent legs of adjacent dipole antenna elements may also be positioned and shaped to provide increased capacitive coupling between the adjacent dipole antenna elements.